B.9A Evidence of Common Ancestry on level – 02

What is common ancestry?

The theory of common ancestry states that all living things on Earth are related to a single type of living thing from long ago. Over time, these original living organisms changed and developed into different species. These changes could have been caused by mutations in DNA. Other changes could have been caused by environmental differences that favored certain traits in some organisms. This made them better able to survive and have offspring. The geography of an area, including stream, rivers, valleys, and mountains may have separated organisms, making it impossible for them to mate with one another. This isolation could lead to each group to developing their own changes over time and becoming different species.

What is the evidence of common ancestry? 

Biogeography and Fossils

Biogeography tells where on Earth organisms live, both in past and present times. Fossils are found in layers of sedimentary rock. Organisms die and are covered over with gravel, sand, and other sediment. The soft tissues of the organism dissolve. Minerals in the sediment surround the harder tissues and make a kind of mold of these structures. Fossils of shells, bones, feathers, hair, leaves, stems and other structures have been found.

Species that are related are usually found living closely to one another. Fossils found in an area often have remarkably similar structures to the species currently living in that area. Often, fossils of similar organisms are found in different layers of rock. By examining these fossils, scientists can see the similarities and changes in organisms over time. These changes can show the shift from one species into a new species. Scientists can also identify the ecosystems and habitats that extinct organisms once occupied by looking at the types of fossils found in each of the rock layers.